Method of treating aluminum oxide



Patented Aug. 5, 1930 UNITED STATES PATENT OFFICE THOMAS AUSTINHITGHELL, OF DENVER, COIORADO, ASSIGNOR T LAFAYETTE I.

HUGHES, OF DENVER, COLORADO METHOD or 'rnnn'rmo ALUMINUM OXIDE No. Drawing. Original application filed August so, 1922, smu No. 585,311. Divided and this application filed July 29, 1927.

My invention relates to the art of treating I aluminous bearing materials to recover valuable products therefrom and more 'particu larly to a method of treating crude alumi-' num oxide which occurs in nature in various forms, such as bauxite, diaspore, gibbsite, corundum and emery, associated with impurities such as silica, ferric oxide, titanic oxide, etc. This case is a division of my copending application Serial No. 585,311 filed August The main object of my invention is to provide an eflicient and economicalmethod of recovering substantially pure aluminum'oxide from common alumina bearing materials,

which may be siliciousand contain various otherimpurities, and at the same time producing valuable .by-products from the reagents employed. Further objects will be apparent in the following disclosure.

' In the-treatment of bauxite, it has been proposed to calcine it with calcium carbonate to form calcium aluminate which may subsequently be converted to a soluble sodium tage of my dilslp aluminate by leachingjwith 'a sodium car bonate solution. It, however, is foundthat the calcination of bauxite with calcium carbonate results in a hard vitreous mass which i is not easily ground or leached, this condition 'being presumably brought about by the presence of silica which forms calcium silicates and serves as a bond or a flux to make a solid mass of the material. I As a result of my experimentation, I have found that an alkaline earth metal aluminate may be formed from crude aluminum oxide, .isuchl as occurs in clays and other materials, and may contain a large amount of silica as well as other impurities, by calcining it with a carbonate of such metal and that the calcine will be found in an easily leached condition, thereby resulting in a high yield, if a small amount of an alkaline earth metal sulfate, such as calcium sulfate, is interspersed throughout the aluminate. In a subsequent leaching operation, preferably with an alkali metal carbonate solution, such as sodium carbonate, "the calcium sulfate will bi! transposed to calcium carbonate and soluble.sodium sulfate formed throughout the .by forming a cylic process.

Serial No. 209,397.

calcine, thereby forming pores or channels WhlCll permit the carbonate solution to attack the mass readily. The presence of the alkaline earth metal sulfate appears to prevent the formation of a vitreous mass, such as a calcium aluminum silicate, and keeps the product light and easily grindable'. The other elements of the alkaline earth group, barium, strontium and magnesium, may be employed in place of calcium, it being understood that the subsequent treatment after calc1nat1on will depend upon the nature of the original ingredients to be calcined. For example, if soluble magnesium sulfate is formed in the calcine, it will preferably be washed out with water before leaching with the sodium carbonate solution, thereby eleminat ng the formation of'large amounts of sodlum sulfate. Barium sulfate on the other hand is insoluble in the sodium carbonate s ollution and remains with the residue durnng leachlng, whereas calcium sulfate is tiansposedto a carbonate during this step.

I have also found that by taking advanovery of the function of such interspersed ater'ial, the furnacing operation may be utilized'to form desired by-prodnets and to convert cheap minerals or such waste materials as ferrous sulfate or aluminum sulfate into valuable commercial salts, and to-this end I employ such reagents'and so carry on my process as to form the desired alkaline earth metal sulfate interspersed throughout the calcine and thereafter transpose the undesired ingredients to more useful materials or recover the original salts formed during calcination, -as seems best.

By employing a carbonate instead of other com ounds of alkaline'earth metals to form the. aluminate, I insure an evolution of carbon dioxide during the reaction which aids in keeping the calcine in an easily leachable condition and furnishes a gas for later use in the recovery of sodium carbonate and the precipitation of aluminum 'hydroxid, there- In accordance with my invention I propose to calcine bauxite, diaspore and similar sulfate free, alumina'bearmg clays or minerals 1n the presence of an alkaline earth material and a non-alkali metal'compound containing the sulfate radical which is capable of reacting with the alkaline earth material to form a sulfate, and the ingredients are preferably so proportioned as to form a mono-alakaline earth metal aluminate with all of the alumina present and a basic alkaline earth metal sulfate interspersed throughout the mixture.

The alkaline earth material, which is preferably a carbonate of calcium, barium, strontium or magnesium, taken either separately or in combination, is utilized preferably in a molecularly equivalent amount to combine with all of the alumina present to form a mono-alkaline earth metal aluminate therewith and to combine with all of the silica, iron oxide, titanium oxide, and other associated reactive impurities to form alkaline earth metal silicates and other compounds therewith. An additional amount of alka-- line earth metal carbonate or other suitable compound is employed to combine with all of the added sulfate radical to form the interspersed alkaline earth metal sulfate and with any reactive metal, such as iron or aluminum, which may be present. The nature of the added ingredients will be predetermined in accordance with the soluble or insoluble end products which may be desired. Since I ordinarily treat the calcine in a subsequent step by leaching itvwith an alkali metal carbonate, such as a sodium carbonate solution, to form soluble sodium aluminate and insoluble calcium carbonate, I prefer to employ such sulfates and metal compounds as will not permit the formation of relatively cheap and undesirablematerials, during the leaching operation but which give valuable metal sulfates as by-products.

The materials are prepared for the calcination operation in'accordance with well known methods, as by grinding to a finely divided'condition, and suitably mixing them wet or dry. The mixture may be calcined either in dry form or as a wet slurry, at a suitable temperature-,such as 1300 C., after which the resulting calcined material may be stored or fed to a granulating device, using water or sodium carbonate solution for the partial extraction of the aluminate. This slurry is; then carried to the leaching and decantation system, such as Dorr agitators and thickeners, for the separation of the sodium aluminate solution from the residue, after which ahlminum hydroxid. may be suitably precipitated therefrom as by passing carbonrdioxide gas through the mass. The.

residues maybe treated as desired to recover valuable ingredients and. the hydroxid may by well known methods."

be converted to the metal or the oxide form Ofthe various metal sulfates or minerals cont'alning the same which are available and may be convertedto more valuable materials by my process, I prefer to employ sulfates of iron, aluminum, zinc andlead, but I may employ chromium, cobalt, nickel and manganese if desired and such materials are to be considered as full equivalents in this process. It is tobe understood that the metal sulfates which I may employ exclude those in which the metal is an alkaline earth metal or an alkali metal. The material must be one which will react with the alkaline earth metal carbonate to form a sulfate interspersed throughout the calcine. For example, aluminum sulfate or minerals bearing aluminum sulfate, such as alunite, or the alums, may-be incorporated with the alkaline earth metal carbonate and crude aluminum oxide ore. In this case, the alkaline earth metal carbonate, preferably calcium carbonate, is correctly proportioned to form monoalkaline earth metal aluminate with all of carbonate is used, an insoluble barium sulfate is formed, this salt remaining undi ssolved during the leaching operation. The barium compound is preferably added in an amount equivalent to the S03 present, the alumina of the aluminum sulfate being taken care of by an excess of calcium carbonate over that required by the alumina in the bauxite ore. If other alkaline earth metal carbonates are employed, a soluble metal sulfate, such as magnesium sulfate, is afterwards obtained from the filtrate. For example, I may cmploy dolomite and limestone for t-hecarbonates with the materials ro ortioned as follows: P p

Parts by weight Bauxite .Q. 100 Calcium carbonate 80 Magnesium carbonate 8 Aluminum sulfate 1O Calcination of this mixture results in the formation of calcium aluminate and magnesium sulfate. The latter along with any other e soluble salts may be washed from the. calcine to from'calcium sulfate. Here again, in so to react therewith. As an example, I may use:

Parts by weight Bauxite 100 Calcium carbonate Ferrous sulfate 10 Calcination of this mixture and subsequent 'ment. If magnesium carbonate or dolomite is used, a soluble magnesium salt is obtained by washing with water, before the step of leaching with the soda ash.

' Zinc and lead salts may be similarly employed to furnish the sulfate, or carbonates of these metals combined with other sulfate bearing materials such as sulfuric acid may be used in molecular proportions with the alkaline earth metal carbonate and alumina ore to'produce the desired end products.

If other salts,'such as chlorides and nitrates,of the alkaline earths and metals are availableas cheap raw materials, they may be employed together with a sulfate bearing material, such as sulfuric acid, to provide a metal and a sulfate radical for the reaction. If the acid radical of the salt used is volatile it may be collected and recovered from the furnace gases. Likewise, if soluble salts are formed, they may be crystallized out the same as any soluble metal sulfate which-may be produced during the reaction, or they are otherwise suitably separated from the cal-' cined mass.

It should be understood that the reactions which actually take place in practice are probably more complex than as' described, but it is immaterial what .ennipounds are formed during calcination 'sa;;; f.long as the I desired end products are' obtained. I calculate the proportions of the essential elements for the original mixture to insure sufficient alkaline earth material for substan tially completing theyreactions and to give such end products as are'commercially desirable. I am not limitedto any particular amount of alkaline earth metal sulfate, but merely use sufficient sulfate as determined by the analysis of the alumina ore to give a non-vitreous and easily leached calcine as well as by the amount of sulfate desired as an end product.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is: y

1. A method of treating crude aluminum oxide comprising the ste of calciningthe oxide with an alkaline eart metal compound, which is capable of reacting "with aluminum oxide to form an aluminate, and the sulfate of a non-alkali metal which is capable of reacting with the alkaline earth metal compound to form alkaline earth metal sulfate, said alkaline earth metal compound being sufficient in amount to combine with all of the alumina and its reactable impurities and aluminate having alkaline earth metal sulfate interspersed throughout the calcine.

2. A method of treating crude aluminum oxide comprising the steps of mixing the oxide with a carbonate of an alkaline earth metal and a compound containing a non-alkali metal base and the sulfate radical which is capable of reacting with' the carbonate to form an alkaline earth metal sulfate, the

all of the sulfate radical present to form an carbonate being present in a suitableamount to form an aluminate of the alkaline earth metal with all the alumina present, to com-- 7 bine with the associated reactive impurities and to react with all of the sulfate radical to form a sulfate of the alkaline earth metal interspersed throughout the calcine, and calcining the mixture to form the aluminate and sulfate.

3. The method of treating crude aluminum oxide comprising the steps of mixing the oxide with an alkaline earth metal carbonate in a chemically equivalent amount to form a mono-alkaline earth metal aluminate with all of the alumina present, and with equivalent proportions of a compound containing a nonalkali metal base and the sulfate radical and an alkaline earth metal compound capabie of reacting to form an alkaline earth metal sulfate, calcining the mass to form an intimate mixture of the alkaline earth metal aluminate and sulfate and subsequently recovering products from'the calcine. p

4;. The method of treating crude aluminumoxide comprising the steps of mixing the oxide with the sulfate of a non-alkali-met'al and an alkaline earth metal carbonate which are capable of reacting to form an alkaline earth metal aluminate and an alkaline earth metal sulfate, calcining the same to form an intermixture of aluminate and. sulfate and subsequentl alkali meta soluble alkali metal aluminate therefrom.

5. The method of treating crude aluminum oxide comprising the steps of calcining the oxide with alkaline earth metal carbonate and a sulfate of a metal selected from the group consisting of iron, aluminum, zinc, lead, chromium, cobalt, nickel and mangaleaching'the calcine' with an carbonate solution to form a. p

nese which is capable of formingalkalme.

earth metal sulfate and alkaline earth metal aluminate, and subsequently treating the calcine to recover an aluminum compound therefrom. i

6. The method of treating crude, aluminum oxide comprising the steps of mixing the oxide with alkaline earth metal carbonateselected from the group consisting of iron, aluminum, zinc, lead, chromium, cobalt, nickel and manganese, said carbonate being present in an amount sufficient to form alkaline earth metal compounds with all of the other reactive ingredients, and thereafter calcining the mass to form alkaline earth aluminate, sulfate and other compounds.

7. The method of treating crude aluminum oxide comprising the steps of calcining the oxide in the presence of aluminum sulfate and an alkaline earth metal compound capable of reacting therewith to form alkaline earth metal sulfate and aluminate, and subsequently treating the calc'ne to recover an aluminum compound there rom.

8. The method of treating crude aluminum oxide comprising the steps of mixing the oxide with alkaline earth metal carbonate and a material containing the element aluminum and the sulfate radical, the-alkaline earth metal carbonate beingpresent in amount sufficient to combine with all of the alumina and the sulfate radical, calcining the mixture to form alkaline earth metal aluminate and sulfate intimately mixed and subsequently recovering an aluminum compound from the calcine.

9. The method of treating crude aluminum.

oxide comprising the steps of mixing the oxide with aluminum sulfate and an alkaline earth metal carbonate, the amount of the latter being sufiicient to react With all of the alumina and the sulfate radical present as Well as with the reactive impurities, calcining the mixture to form alkaline earth metal aluminate and sulfate, washing the calcine with water to remove soluble compounds, leaching with an alkali metal carbonate solution to form a soluble aluminate and subsequently recovering an aluminum compound from the solution.

10. The method of treating crude aluminum oxide comprising the steps of mixing the oxide with alkaline earth metal carbonate in equivalent amounts to form a monoalkaline earth metal aluminate with all of the alumina present, and with aluminum sulfate and magnesium carbonate in equivalent proportions to form.magnesium aluminate and magnesium sulfate with all of the aluminum sulfate present, calcining the mixture to form alkaline earth metal aluminate and sulfate,

and thereafter recovering products from the calcine.

Signed at Denver, Colorado, this 21st day of July, 1927.

. THOMAS AUSTIN MITCHELL. 

